Getting 0 Volume for object
μm is Micrometre, one thousandth of a millimetre (0.001 mm or about 0.000039 inch).
If you try to calculate the volume of 81.38x23.00x59.80 um it will be around 0,0001mm3 or 0,0000001cm3 that is to small and rounded.

If you want to measure object in imperial units you need to go to scene tab and select this unit system from presets: